Apparatus for fractionating finely divided material



J. F. MILLER Aug. 2, 1955 2 Sheets-$heet 2 APPARATUS FOR FRACTIONATINGFINELY DIVIDED MATERIAL Filed Aug. 10 1951 INVENTOR \JQmeJ an /b9 M715,

APPARATUS FOR FRACTIONATING FINELY DIVIDED MATERIAL James F. Miller,Pittsburgh,

States of America as the Army Application August 10, 1951, Serial No.241,376 2 Claims. (Cl. 2tl9-142) Pa., assignor to the United representedby the Secretary of This invention relates to apparatus for separatingor fractionating finely divided or powdered material. Such apparatus issometimes termed an elutriator.

Among the insecticide dusts which have had large scale military usageare those composed of DDT in a diluent consisting of pyrophyllite(aluminum silicate) and 10% DDT in talc as a diluent. Diluents, ofcourse, are used for providing the most economical distribution of theactive ingredient. As a rule, the physical performance characteristicsof an insecticide dust are principally those of the diluent, and thebiological activity of the insecticide is a function of the physicalperformance characteristics of the dust. These characteristics depend onvarious factors, one of the most important being particle size. Theparticle size distribution of a dispersed dust has a great influence onsuch properties as fall rate, degree of agglomeration of the dispersedparticles, ease of dispersion, adhesion to dry surfaces, and flotationon water. These facts make it desirable to fractionate diluents byparticle size in order to study the effect of particle size on thetoxicity and other properties of the dust.

Elutriation equipment available on the market is considered to be toolarge and too expensive, one wellknown particle size analyzer, completewith accessory equipment, being priced at about one thousand dollars in1946. Another type of classifier employing a cyclonic separation ofpowdered materials was tested carefully, and small samples of thefractions obtained were suspended in alcohol and examinedmicroscopically, using a calibrated filar micrometer eyepiece or aregular eyepiece containing a calibrated Whipple disc; but under thebest operating conditions, satisfactory separation of the fractions wasnot obtained.

The present invention provides an elutriation system which permitscontinuous operation, which is relatively simple in construction andinexpensive to manufacture, and which effects a satisfactory separationof the fractions, e. g., below 5 microns, 5-10 microns, lit-20 microns,20-30 microns, 30-45 microns, 45-65 microns, and above 65 microns.Another general object is to provide an elutriation apparatus whichrequires little attention from the operator, once a run starts. Morespecific objects are to provide apparatus which makes a given runwithout change in the air velocity, and which separates the largestparticles first, then the next largest particles, and so on. Otherobjects will be apparent from the following description of the preferredembodiment of the invention shown in the accompanying drawings forming apart of this specification.

In said drawings,

Fig. l is a sectional elevation of the assembly of elutriator tubes andcertain associated parts, showing diagrammatically the tube-vibratingmeans;

Fig. 2 is a cross section on line 2-2 of Fig. 1;

Fig. 3 is a detail in vertical section, showing a joint in one of thetubes;

Fig. 4 is a vertical section through end of one of the elutriator tubes;

Fig. 5 is a cross section on line 5-5 of Fig. 4;

Fig. 6 is a cross section on line 6-6 of Fig. 4; and

Pig. 7 is a cross section on line 7-7 of Fig. 4.

In general, the air elutriation apparatus includes a plurality ofvertical elutriator tubes or settling chambers of increasing diameterconnected in series, a source of compressed gas, preferably air, meansfor feeding a charge into the apparatus, and filtering means placed atthe outlet of the largest tube. Between the source of compressed air andthe elutriation apparatus an air control and cleaning system isinterposed, but as the latter system forms no part of the presentinvention, it is not shown. The air control and cleaning system mayinclude, for example, a Nullmatic Pressure Regulator, Air Filter andFlow Controller, manufactured by the Moore Products Co., Philadelphia,Pennsylvania, and a Flowrator, such as is sold by the Fischer and PorterCo, Hatboro, Pennsylvania, all assembled and mounted on a fiat uprightpanel. With such a system, the elutriator tubes are assured a supply ofclean air under con stant pressure.

While various arrangements of elutriator tubes may be employed, jointedmetallic tubes are preferred for ease of assembly and disassembly.Referring to the drawings, i prefer to have the smallest tube 11 of oneinch outside diameter, the second 12 of 1 /2 in. outside diameter, thethird tube 13 of 2 in. outside diameter, the fourth tube 14- or" 3 in.outside diameter, the fifth tube 15 of 6 in. inside diameter, and thesixth tube 16 of 12 in. inside diameter. All six tubes may be about 46long and preferably are cylindrical except at their upper and lowerends, which are frusto-conical, with vertex angles of about 45".However, the smallest tube it does not have a frusto-conical lower end.

The joint of the largest tube 16, which is representative of all thetube joints, is shown in Figs. 2 and 3. As there seen, tube 16 comprisesan upper section 16a and a lower section 16b whose edges are abuttedtogether, the two sections being held by bolts it) passed throughannular flanges 2i and 22 secured respectively to said upper and lowersections and extending outwardly therefrom at right angles. The lowerflange 22 is welded to a circular collar or band 23 which encloses theabutted edges of the joint and is in turn welded to the lower section16b. Other joint constructions may, of course, be used; whatever theconstruction, it should permit easy disassembly of each tube and yetassure a tight joint.

Each of the tubes has its upper frusto-conical end con nected with ashort pipe 25 whose upper end is coupled by a union 26 to a bent pipe27, the latter pipe being welded at its upper end to a Y-coupling 28. Acap 29 is screwed or welded on the upper end of each Y- coupling toclose the same. The other arm of each Y-coupling is welded or otherwisesecured to the upper end of a vertical pipe 3t) which extends downbetween two of the elutriator tubes to a fitting (to be described)discharging into the lower end of the larger of the two elutriatortubes. The intake or feed pipe for the smallest tube 11 is indicated at32, and a small dust receptacle or hopper is shown diagrammatically at33 (Fig. l) to permit manual or other dumping into the system of thecharge of dust to be fractionated. A continuous feed charging device maybe used if large samples are continually run. At the upper and dischargeend of the largest tube 16, a vertical pipe 34 is coupled by a union 35to an inclined pipe 36, a Y-coupling 37 is secured to the upper end ofpipe 36, a cap 38 closes the top of the Y-coupling, and a downwardlyextending straight the lower or inlet pipe 39 receives the dischargefrom Y-coupling 37. Pipes 34 and 36, union 3S, Y-coupling 37, cap 38 andpipe 39 are all larger than the corresponding parts coupled to the smalltubes 11-15. If pipes and connected parts are one-fourth inch tubes, Iprefer that pipe 34 and connected parts be of the %1 in. size. It willbe noted that the described arrangement of pipes and Y- couplingsprovides conduit means coupling the top of each tube with the bottom ofthe next larger tube of the series, and that no surfaces are providedfor the collection of dust, the nearly vertical pipes rising from thetops of the elutriator tubes and the Y-couplings insuring a flow ofdust-laden air without collecting dust at any particular point. TheY-couplings also facilitate disassembling the conduit means forcleaning.

At the lower end of pipe 39 filtering means in the form of an extractionthimble 40 is secured, for example by a rubber stopper (not shown)fitting on the end of pipe 39, and masking tape (not shown) securing andsealing the thimble on the rubber stopper. tion thimble is made of aspecial porous paper, known as fat free filter paper, seamless, ofsingle or double thickness, or it can be made of alundum or otherairpermeable materials with pore diameters of less than oneone-hundredths of a micron. The very finest particles obviously willcollect on the inner walls of the extraction thimble, while the air,substantially free of all particles, will pass out through the walls ofthe thimble to the atmosphere.

Now referring to Figs. 4, 5, 6 and 7, the lower end of each elutriationtube is connected with an intake pipe 30 by means of a two-part fittinghaving a horizontal air passageway 46 leading to the underside of anozzle 47 located in the extreme lower end of the elutriation tube, saidnozzle having a plurality of ports 48 arranged in a circular series.There may be eight such ports each one-sixteenth of an inch in diameter,equally spaced in the nozzle, all the ports being disposed at the sameangle as the walls of the frusto-conical lower end of the elutriationtube (preferably 22 /2 degrees). The two parts of fitting 45 may betemporarily secured together as by screws (not shown), and a sealingcompound 50 may seal the fitting on the elutriation tube and on the endof intake pipe 30.

To obviate corrosion of the inner surfaces of the apparatus which wouldretain some of the dust, all the described parts may be made ofstainless steel or a similar metal or alloy. Such a material will alsofacilitate grounding the apparatus to remove electrostatic charges. :2

As shown in Fig. 1, each elutriator tube has a wire connecting it with aground, for example a water pipe not shown. The pipe connectionscoupling each pair of tubes may be separately grounded. To vibrate theelutriator tubes to prevent adherence of dust to their inner walls, asmall electric vibrator 57 is located adjacent each tube, each vibratorbeing illustrated as an electric bell whose bell has been removed sothat its clapper 58 will hammer the walls of the tube. Another form ofvibrator which may be used is shown in the P. S. Roller Patent No.2,019,507 dated Nov. 5, 1935. Because of the unpleasant noise of thevibrators, the entire assembly preferably is housed in a box or casing(not shown) having sound-absorbing walls. In lieu 3 of vibrators, aBoerner shaker (not shown) may be connected to the bottoms of all thetubes to shake them and thus prevent channeling of the air through thesample being fractionated and through the fractions collecting in thetubes.

In a calibration run of the described apparatus, using industrial flyash (which contains, in general, about spherical particles in the sizerange of from less than one micron to about 300 microns) the followingresults were obtained:

The extrac- (1. TABLE I Percentage by weight of a given particle sizefound in each tube Particle Size Tube Tube Tube Tube Tube Tube Range(mu) 11 12 13 14 15 1e Thlmble Above 65 100.00

An inexperienced operator us1ng industrial fly ash obtained thefollowing results:

TABLE 11 Percent of Recovered Material Fraction (microns) Usually 50 gm.samples were charged and the apparatus was then run about 72 hours.However, it is possible to charge 50 gm. of dust, and start elutriation,then after two hours or so, shut off the apparatus, feed another 50 gm.of dust, and resume elutriation for another two hours, and so on untilthe desired amount of dust 7 had been charged, concluding the run byabout hours fat of elutriation. In this way several pounds of dust maybe included in one run. The above referred to analyzer of the prior art,on the other hand, handles only about 15 gm. of dust in each run,separates only one fraction at a time, may require an adjustment of airflow between each fraction, and demands almost constant attention of theoperator during fractionation (2 /2 hours). With this prior artapparatus, the total time for fractionation of a one pound sample willbe about 10 eight hour days, including setting up and. cleaning; andduring all that time, almost constant attention of an operator isrequired. The present apparatus requires the attention of the operatoronly when charging and during occasional checking of air flow andreplacing thimbles; a total running time of 72l20 hours is all that isneeded (the one pound charge requiring about 120 hours), followingwhich.

about eight hours time is necessary for removing fractions, cleaning,reassembling, recharging, and readjustment of air flow for a new run.Furthermore, the described apparatus may be run 24 hrs. a day sinceusually no attention is required during a run. Finally, noprefractionation run is necessary, whereas with each new material theprior art apparatus must be run about five hours, under constantsupervision, to determine the proper running time for completeseparation of each fraction.

While particular mention has been made of diluents and insecticidedusts, the described apparatus may be used in connection with theanalysis of cements, volcanic ash,- diatomaceous earth, Cottrellprecipitator dust, pulverized coal, carbon, limestone, gypsum, quartz,shale, feldspar, mica, flint, salt, silica gel, talc, flake alumina,kaolin, China clay, magnetite, pigments, diatomite, battery lead oxide,organic dyes, wood flour, free-flowing sulphur, and other materials.

Obviously changes may be made in the dimensions, proportions, and numberof parts, and their relative positions, without departing from theinvention as defined in the appended claims.

What I claim is:

1. A continuous run apparatus for fractionating finely divided materialconsisting of a plurality of vertical elutriation tubes of differentdiameters arranged in ascending order, conduit means connecting theseveral tubes in series with the top of each tube connected through theconduit means with the bottom of the next larger tube of the series, asource of compressed gas coupled to the bottom of the smallest tube ofthe series, means for introducing the material to be fractionated intothe apparatus near the connection with the source of compressed gas, agas discharge outlet with filtering means connected with the upper endof the largest tube of the series, the several tubes each consisting oftwo separable abutted parts, flanges being secured to and projectingoutwardly from each of said parts, the flanges being separated when theparts are abutted, and bolts passing through the flanges to secure theseparable parts together, a collar or band being fixed to one of theparts of each pair and enclosing the abutted edges of the joint so as toaid in sealing the same.

2. A continuous run apparatus for fractionating finely divided materialcomprising a plurality of elongated verti cal elutriation tubes ofdifierent diameters but of the same height and arranged in ascendingorder, the lower ends of all the elutriation tubes except the smallesttube being frusto-conical, conduit means connecting the several tubes inseries with the top of each tube connected through the conduit meanswith the lower end of the next larger tube of the series, a source ofcompressed gas coupled to the lower end of the smallest tube of theseries, means for introducing the finely divided material into theapparatus near the coupling of the source of compressed gas with thesmallest tube of the series, a gas discharge outlet with filtering meansconnected with the upper end of the largest tube of the series, each ofsaid conduit means including a fitting secured to the extreme lower endof the next larger elutriation tube of the series, each fitting having agas passageway and having its upper part surrounding the extreme lowerend of the elutriation tube and forming a gas-tight joint therewith, anozzle located inside the elutriation tube at the extreme lower end andhaving a plurality of ports arranged in a circular series and directedupwardly at the same angle as the walls of the frusto-conical lower endof the elutriation tube; the upper ends of said ports being located veryclose to the lower end of the frusto-conical end of the elutriationtube.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Bulletin 2055 of American Instrument Co., Inc., 8010 8020Georgia Avenue, Silver Spring, Md., October 1937. Four pages. (Copy inDiv. 55.)

Taggart: Handbook of Mineral Dressing, pp. 19-116, pp. 19-111. 1945.(Copy in Div. 55).

Taggart: Handbook of Mineral Dressing, pp. 19-112. J. Wiley & Sons,Inc., N. Y. 1945. (Copy in Div. 55.)

pp. 19-115, J. Wiley & Sons, Inc., N. Y.

1. A CONTINUOUS RUN APPARATUS FOR FRACTIONATING FINELY DIVIDED MATERIALCONSISTING OF A PLURALITY OF VERTICAL ELUTRIATION TUBES OF DIFFERENTDIAMETERS ARRANGED IN ASCENDING ORDER, CONDUIT MEANS CONNECTING THESEVERAL TUBES IN SERIES WITH THE TOP OF EACH TUBE CONNECTED THROUGH THECONDUIT MEANS WITH THE BOTTOM OF THE NEXT LARGER TUBE OF THE SERIES, ASOURCE OF COMPRESSED GAS COUPLED TO THE BOTTOM OF THE SMALLEST TUBE OFTHE SERIES, MEANS FOR INTRODUCING THE MATERIAL TO BE FRACTIONATED INTOTHE APPARATUS NEAR THE CONNECTION WITH THE SOURCE OF COMPRESSED GAS, AGAS DISCHARGE OUTLET WITH FILTERING MEANS CONNECTED WITH THE UPPER ENDOF THE LARGER TUBE OF THE SERIES, THE SEVERAL TUBES EACH CONSISTING OFTWO SEPARABLE ABUTTED PARTS, FLANGES BEING SECURED TO AND PROJECTINGOUTWARDLY FROM EACH OF SAID PARTS, THE FLANGES BEING SEPARATED WHENMECHANISM FOR SHIFTING SAID CLOSURE MEMBER, RELEASABLE ACTIVATING MEANSPRESET BY SAID TESTING MEANS MANIFESTING A PREDETERMINED CLASS OFARTICLE OF A GIVEN SAID FORM, HOLDING MEANS PRESET IN COORDINATION WITHMOVEMENT OF SAID GIVEN FORM AWAY FROM THE TESTING MEANS AND OPERABLE FORRELEASING SAID ACTIVATING MEANS IN READINESS FOR A NEXT SUCCEEDINGOPERATION THEREON, MEANS OPERABLE THROUGH SAID PRESET HOLDING MEANS INCOORDINATION WITH FURTHER MOVEMENT OF SAID GIVEN FORM INTO ARTICLEEJECTING POSITION WITH RESPECT TO SAID RECEPTACLE FOR ACTUATING SAIDMECHANISM AND THEREBY TO SHIFT SAID CLOSURE MEMBER TO CLOSE ONE SAIDCHAMBER INLET OPENING AND TO OPEN THE OTHER FOR RECEIVING AN ARTICLEEJECTED FROM THE GIVEN FORM INTO SAID MOUTH.